Commercial aircraft commonly comprise a pressurized cabin arranged in a fuselage and supplied with conditioned air through an environmental control system. Often, the environmental control system comprises at least one air cycle machine as a refrigeration unit, which is often referred to as an air conditioning pack and is supplied with pressurized air tapped from main engines of the aircraft. The pressurized air is routed through a series of turbines, heat exchangers and compressors and allows to create relatively high flow rates of conditioned air with a certain temperature and pressure. Hence, cooling and pressurization of the cabin are accomplished through the air-conditioning pack at the same time.
However, tapping air from a compressor section of a jet engine leads to decreasing the efficiency of the respective engine, as fuel is consumed for compressing air for supporting the combustion and thrust, while a part of the air is taken away from this process by the environmental control system. Other techniques are known, which are based on supporting an air-cycle process and comprise additional cooling means or additional compressors.
For example, international patent document WO 2011/147977 A2 shows a system for air conditioning an aircraft cabin, comprising at least one cooling circuit, at least one compressed-air line and at least one compressor for compressing air, wherein the cooling circuit is connected to the compressor by way of the compressed-air line, and wherein the compressor is drivable independently of bleed air.
Still further, electrical environmental control systems are known, which are operable without bleed air and receive a flow of fresh air from ram air inlets.